Passos et al. 2018 performed detailed comparisons between the holotype of A. balzani (Fig. 1; Table 1) and two species reported as occurring in the Yungas region of Bolivia, Atractus emmeli (Boettger 1888) and A. major Boulenger 1894 (Boulenger 1896: 645; Fig. 3). We can distinguish A. balzani from A. major by having an inconspicuous canthus rostralis, six supralabials, and the first four infralabials contacting chinshields (vs. very conspicuous canthus rostralis, seven supralabials, and first three infralabials contacting chinshields). By contrast, there is no feature in external morphology that unequivocally distinguishes A. balzani from A. emmeli, and Boulenger (1898) based his description of A. balzani mainly on its general color pattern, the presence of one postocular and 17 dorsal scales rows (supposedly counted on the midbody). Although inconsistent in the A. emmeli populations, all these features are polymorphic certainly in the Bolivian and Peruvian samples (Figs. 1–2; Table 1). In addition, the taxonomy of the Atractus emmeli complex was recently reassessed through an integrated approach (P. Passos et al. in prep.), with a considerable increase of the phenotypic variability range previously reported for the nominal species (e.g., McCoy 1971; Salazar-Bravo et al. 2010). Nonetheless, in the aforementioned studies, the authors were not able to examine the holotype of A. balzani, but now, with new data made available from its holotype, it is possible to infer the taxonomic status of the species. The only apparent difference distinguishing both species is the number of dorsal scale rows at midbody, being 15 in A. emmeli and 17 in A. balzani. However, Peters & Orejas-Miranda (1970: 25) reported one individual female of A. emmeli—from an unknown origin—with 17 dorsal scale rows, seven supralabials, two postoculars, 188 ventrals and 22 subcaudals. Additionally, we also corroborated the presence of polymorphic dorsal scale rows counts in A. emmeli based on two other specimens from Peru (MUSM 2313 provenance unknown and MUSM 27402 from Trompeteros, department of Loreto), which retained 17/17/17 and 15/17/17 dorsal scales, respectively. The A. balzani holotype is also polymorphic with respect to its dorsal scale rows, displaying 14/17/16. In addition, the differences in color pattern between the A. balzani holotype, the lectotype of A. emmeli (Fig. 1) and additional specimens of A. emmeli from Bolivia, being the pale occipital band, a dorsum which is uniformly black and belly which is almost fully cream are also polymorphic in the Bolivian populations of A. emmeli (Fig. 2). Thus, it is not possible to distinguish both species based on any of the traits mentioned above, and we conclude that the best taxonomic decision to be made at this time is to place A. balzani in the synonymy of A. emmeli.

Comment

Etymology

Named after Dr. Luigi Balzan (1865-1893), an Italian naturalist and collector of the holotype.